The present invention relates, according to an aspect thereof, to an adaptive cruise control system for a motor vehicle comprising a forward looking object detecting means arranged to simultaneously detect several target objects moving in the predicted path and adjacent paths of the equipped vehicle. The means are further arranged to continuously monitor velocity and distance to each of said target objects.
It further comprises processing means arranged to process signals from said detecting means to provide information of distance to and relative speed of vehicles travelling in front of the equipped vehicle, wherein the processing means further is arranged to repeatedly generate velocity control signals based on the information of distance to and relative speed of vehicles travelling in front of the equipped vehicle. Also comprised is means to control velocity of the equipped vehicle in response to the control signals from the processing means.
The present invention also relates, according to an aspect thereof, to a method for adapting the velocity of a vehicle equipped with the above described system.
There are presently several adaptive cruise control systems, or autonomous cruise control systems, available for comfortably controlling a vehicle to keep a distance in time (nine-gap) to a leading vehicle. These systems generally use either a radar or laser setup allowing the vehicle to slow when approaching another vehicle and accelerate again to the preset speed when traffic allows. ACC technology is widely regarded as a key component of any future generations of intelligent cars. Laser-based systems are significantly lower in cost than radar-based systems; however, laser-based. ACC systems do not detect and track vehicles well in adverse weather conditions nor do they track extremely dirty (non-reflective) vehicles very well. Laser-based sensors must be exposed, the sensor (a fairly-large black box) is typically found in the lower grille offset to one side of the vehicle.
Radar-based sensors can be hidden behind plastic fascias, however, the fascias may look different from a vehicle without the feature. For example, some car producers package the radar behind the upper grille in the centre; however, the grille on such applications contains a solid plastic panel in front of the radar with painted slats to simulate the slats on the rest of the grille.
Single radar stems are the most common. Systems involving multiple sensors use either two similar hardware sensors, or one central long range radar coupled with two short radar sensors placed on the corners of the vehicle. There are of course all kinds of combinations available on the market.
From a fuel consumption perspective, performance may deteriorate if the lead vehicle brakes and accelerates more than the tolerance for deviating from the desired “time gap”, as the equipped vehicle would then also brake and accelerate. The experience from this is a negative impact on the fuel consumption from such a system.
In order to solve the above mentioned problem several vehicles can be monitored at the same since the cruise control can be improved if several vehicles are tracked at the same time, allowing the equipped vehicle to avoid, braking/accelerating if it is likely to have to accelerate/brake again in a short time to compensate for the first action.
WO2007/069997 discloses an adaptive cruise control system where one or several vehicles are monitored in order to establish a distance value and a speed target value. The system compares the respective control order generated from the detection of an individual vehicle and selects the order that gives the slowest velocity.
In U.S. Pat. No. 5,629,851 is described an adaptive cruise control system where a sensor senses the distance to several vehicles in front of the equipped vehicle. Each detected vehicle is targeted and the most appropriate target is selected which normally is the closest target which is directly in the path of the equipped vehicle.
Further, U.S. Pat. No. 6,816,084 discloses an adaptive cruise control system for monitoring, several vehicles, wherein the surrounding environment is divided into at least one near zone and at least one distant zone. The position, e.g. lane, speed and distance of each monitored vehicle is determined in relation to a near and a distant zone. The speed is of the equipped vehicle is then adjusted based on the position. The system comprises at least two forward looking sensors for the different zones.
It is desirable to provide an adaptive cruise control system that aims at reducing the negative impact of lead vehicle behaviour by taking into account a group of leading and adjacent vehicles rather than just one. It is also desirable to provide a method for adapting the velocity of a vehicle taking into account a group of leading and adjacent vehicles rather than just one.
The adaptive cruise control system according to an aspect of the present invention for a motor vehicle comprises a forward looking object detecting means arranged to simultaneously detect several target objects moving in the predicted path and adjacent paths of the equipped vehicle. The means are further arranged to continuously monitor velocity and distance to each of said target objects. The system also comprises processing means arranged to process signals from said detecting means to provide information of distance to and relative speed of vehicles travelling in front of the equipped vehicle, wherein the processing means further is arranged to repeatedly generate velocity control signals based on the information of distance to and relative speed of vehicles travelling in front of the equipped vehicle. Means to control velocity of the equipped vehicle in response to the control signals from the processing means is also comprised in the adaptive cruise control system.
The processing means is further arranged to calculate a distance in time from the equipped vehicle to a virtual target vehicle, the distance to and velocity of said virtual target vehicle calculated on basis of the number of vehicles in said group, the spread in distance of the group, and thus the vehicle density of said group, and the variability of positions in the group. The algorithm of the processing means decides from the above parameters on the allowed deviations in time distance, wherein the processing means is arranged to produce a signal to the means for controlling the velocity of the equipped vehicle that is based on the calculated distance in time between the equipped vehicle and said virtual vehicle.
Preferably, the angle is monitored as well as the lateral distance. The monitored vehicles can in the system or method be considered as velocity vectors.
The idea according to an aspect of the invention is to track several vehicles at the same time and use all of them of adaptive cruise control purposes instead of just selecting one of them. A group of targets is more likely to behave “smoother” than a single individual vehicle and the method/system tries to asses this smoothness. Actions that, if unknown, would cause the equipped vehicle to perform actions that would soon have to be corrected, are predicted and considered when controlling the equipped vehicle. The motions of individual vehicles in a group are believed to be highly correlated. Also, all vehicles in a group are not necessarily considered to be equally “important” but are preferably weighted based on for instance distance and speed.
Preferably the signal produced by the processing means to the means for controlling the velocity represents a value of the desired velocity.
In a preferred embodiment of the present invention the processing means is configured to calculate the covariance for all target objects within the detected group, which covariance is used in the algorithm for predicting the behaviour of the virtual target vehicle.
In another preferred embodiments of the present invention the virtual target vehicle is derived to have eco-driving properties.
In yet another embodiment of the present invention the object detecting means comprises a radar unit or a LIDAR unit or a camera unit for establishing a distance value and a velocity value for each of the detected target objects. LIDAR (Light Detection And Ranging) is an optical remote sensing technology that measures properties of scattered light to find range and/or other information of a distant target. The prevalent method to determine distance to an object or surface is to use laser pulses. Like the similar radar technology, which uses radio waves, the range to an object is determined by measuring the time delay between transmission of a pulse and detection of the reflected signal. The term “laser radar” is also in use even though LIDAR does not employ microwaves or radio waves, which is definitional to radar.
Preferably sensors are provided to measure a condition of the road surface. If for instance the road is icy the control signal for the velocity should be based also on a risk analysis with regard to a decreased friction between wheels and road rather than just the velocity of vehicles in front of the equipped vehicle.
Also preferred is an adaptive cruise control system wherein the means to control velocity of the equipped vehicle in response to the control signals from the processing means comprises an engine control means and a brake control means.
Preferably, the adaptive cruise control system further comprises or is combined with a pre-crash system. Such a system warns the driver and/or provides brake support if there is a high risk of a collision. Also, in certain vehicles it is preferred to also have a lane maintaining system which provides power steering assist to reduce steering input burden in corners when the cruise control system is activated.
In a further embodiment the adaptive cruise control system is aided by a GPS. The GPS navigation system provides guidance input to the adaptive cruise control system. For example, on the motorway, the vehicle just in front is slowing down, but with turn signal on and it is actually heading for a highway off-ramp. Normally the adaptive cruise control system would sense the car in front was decelerating and it would simply apply brakes accordingly to slow the equipped vehicle. But a GPS-guided adaptive cruise control system takes into account the approaching highway exit and it simultaneously receives images from a camera. The camera can detect the turn signal from the car ahead. So instead of braking, this new system continues uninterrupted, because it knows that the car in front will exit the lane. For the navigation system it is possible to use various types of map databases. Also, the invention is not limited to the GPS system, other systems could be used. For instance, the Russian GLObal NAvigation Satellite System (GLONASS), the Chinese Compass navigation system or the Galileo positioning system of the European Union.
According to a first embodiment of the method of the present invention for controlling the velocity of a motor vehicle equipped with an adaptive cruise control system, it comprises simultaneously detecting several target objects moving in the predicted path and adjacent paths of the equipped vehicle with a forward looking object detecting means. Further, continuously monitoring velocity and distance to each of said target objects, processing with a processing means the signals from the detecting means to provide information of distance to and relative speed of vehicles travelling in front of the equipped vehicle, using the processing means for repeatedly generating velocity control signals based on the information of distance to and relative speed of vehicles travelling in front of the equipped vehicle, and controlling the velocity of the equipped vehicle in response to the control signals from the processing means.
The method further comprises calculating a distance in time from the equipped vehicle to a virtual target vehicle, the distance to and velocity of said virtual target vehicle calculated on basis of the number of vehicles in said group, the spread in distance of the group, and thus the vehicle density of said group, and the variability of positions in the group, deciding from the above parameters with the algorithm of the processing means on the allowed deviations in time distance, and finally producing a signal with the processing means to the means for controlling the velocity of the equipped vehicle that is based on the calculated distance in time between the equipped vehicle and said virtual vehicle.